The goal of this research is to elucidate the synaptic basis of associative learning. Experiments with vertebrates have shown the essential conditions for stimuli to become associated are: 1) stimuli (CS and US) must occur together in time, and 2) the CS must predict the occurrence of the US. Experiments with invertebrates have shown them to be favorable preparations in which to examine the cellular basis of simple forms of learning such as habituation and sensitization. The aim of the proposed experiments is to use an invertebrate, Limax maximus, to explore the cellular basis of associative learning more characteristic of vertebrates. Behavioral experiments with Limax demonstrate that associative learning in Limax is similar to that observed in vertebrates. That is, food odors can be made aversive following odor-quinine pairings and non-food odors can be made attractive following odor-fructose pairings. Further, the learned association is dependent both on the stimuli occurring in time and the degree to which the CS predicts the US. In addition, the learning both affects the odor-dependent locomotion and modulates feeding. Experiments have shown that a semi-intact preparation is capable of learning using procedures similar to those used with intact animals: pairing of a food taste which normally elicits feeding with a bitter taste results in a selective suppression of feeding only to the taste paired with the US. Also, several feeding motoneurons and a modulatory interneuron have been identified. The goals of this proposal are threefold: Using combinations of anatomical, behavioral, and physiological techniques 1) to identify 'command' and 'convergence' interneurons of the feeding circuit; 2) to analyze the role of olfactory input on feeding; and 3) to characterize the cellular basis of the temporal specificity and predictability underlying the odor-taste associations demonstrated in the intact animal.